#### 12th Standard Physics English Medium Free Online Test 1 mark questions 2020 - Part Four

12th Standard

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Physics

Time : 00:25:00 Hrs
Total Marks : 25
25 x 1 = 25
1. If voltage applied on a capacitor is increased from V to 2V, choose the correct conclusion

(a)

Q remains the same, C is doubled

(b)

Q is doubled, C doubled

(c)

C remains same, Q doubled

(d)

Both Q and C remain same

2. A force of 40 N is acting between two charges in air if the space between then is filled with glass εr = 8. Then the force between then is

(a)

20 N

(b)

10 N

(c)

5 N

(d)

the same and does not change

3. Two copper spheres A and B of same size are charged to same potential. A is hollow and B is solid. Which of the two holds more charge?

(a)

Solid sphere cannot hold any charge

(b)

hollow sphere cannot hold any charge

(c)

both have zero charge

(d)

both have the same charge

4. Which graph shows the variation of electric field E due to a hollow spherical conductor of radius R as a function of distance from the centre of the sphere?

(a)

(b)

(c)

(d)

5. A closed system contains four charges -8.1C, 14.6C, 20.2C and -200 mC. The total charge in the system_______.

(a)

26.5 C

(b)

-173.3 C

(c)

43.1 C

(d)

243.9 C

6. The temperature coefficient of resistance of a wire is 0.00125 per °C. At 300 K, its resistance is 1 Ω. The resistance of the wire will be 2 Ω at

(a)

1154 K

(b)

1100 K

(c)

1400 K

(d)

1127 K

7. A square aluminum rod is 1 m long and 5 mm on edge. What must be the radius of another aluminum rod whose length is 1 m and which has the same resistance as that of square Aluminum rod?

(a)

1.4 mm

(b)

2.8 mm

(c)

4.2 mm

(d)

5.6 mm

8. A flat dielectric disc of radius R carries an excess charge on its surface. The surface charge density is σ. The disc rotates about an axis perpendicular to its plane passing through the center with angular velocity ω. Find the magnitude of the torque on the disc if it is placed in a uniform magnetic field whose strength is B which is directed perpendicular to the axis of rotation

(a)

$\frac { 1 }{ 4 } \sigma \omega \pi BR$

(b)

$\frac { 1 }{ 4 } \sigma \omega \pi B{ R }^{ 2 }$

(c)

$\frac { 1 }{ 4 } \sigma \omega \pi B{ R }^{ 3 }$

(d)

$\frac { 1 }{ 4 } \sigma \omega \pi B{ R }^{ 4 }$

9. The angular. momentum of an electron revolving in second order (n = 2) is

(a)

6.6 x 10-34 Js

(b)

3.3 x 10-34 Js

(c)

2.1 x 10-34 Js

(d)

9.27 x 10-34 Js

10. An inductor 20 mH, a capacitor 50 μF and a resistor 40 Ω are connected in series across a source of emf v = 10 sin 340 t. The power loss in AC circuit is

(a)

0.76 W

(b)

0.89 W

(c)

0.46 W

(d)

0.67 W

11. A transformer

(a)

converts energy

(b)

changes voltage

(c)

changes current

(d)

changes both current and voltage

12. Let E = Eo sin[106 x -ωt] be the electric field of plane electromagnetic wave, the value of ω is

(a)

(b)

(c)

(d)

13. Every source has its own characteristic __________ spectrum.

(a)

white

(b)

emission

(c)

scattering

(d)

absorption

14. A plane glass is placed over a various coloured letters (violet, green, yellow, red) The letter which appears to be raised more is,Two point white dots are 1 mm apart on a black paper. They are viewed by eye of pupil diameter 3 mm approximately. The maximum distance at which these dots can be resolved by the eye is, [take wavelength of light, λ = 500 nm]

(a)

1 m

(b)

5 m

(c)

3 m

(d)

6 m

15. A small piece of wire bent into an L shape with upright and horizontal portion of equal length, is placed with the horizontal portion along the axis of concave mirror whose radius of curvature is 10 cm. If the bend is 20 cm from the pole of mirror, then the ratio of lengths of the image of upright and horizontal position of the wire is

(a)

1: 2

(b)

3: 1

(c)

1: 3

(d)

2: 1

16. Emission of electrons by the absorption of heat energy is called_______emission.

(a)

photoelectric

(b)

field

(c)

thermionic

(d)

secondary

17. What is the energy of a photon of wavelength 6000 Å.

(a)

3.3 x 10-10 J

(b)

4.4 x 10-19 J

(c)

3.3 x 10-19 J

(d)

4.4 x 10-10 J

18. Below the threshold frequency, if the intensity of radiation is increased, the emission of photoelectrons _______

(a)

increases

(b)

decreases

(c)

is zero

(d)

is a constant

19. Mp denotes the mass of the proton and Mn denotes mass of a neutron. A given nucleus of binding energy B, contains Z protons and N neutrons. The mass M(N,Z) of the nucleus is given by(where c is the speed of light)

(a)

M(N,Z)=NMn+ZMp-Bc2

(b)

M(N,Z)=NMn=ZMp+Bc2

(c)

M(N,Z)=NMn=ZMp-B/c2

(d)

M(N,Z)=NMn=ZMp+B/c2

20. J.J. Thomson's experiment demonstrated that

(a)

cathode rays are streams of negatively charged ions

(b)

all the mass of an atom is in the nucleus

(c)

specific charge of electrons is much greater than the protons.

(d)

e/m ratio changes when different gases is placed in the discharge tube

21. Natural uranium consists of _____________ % of U235 and __________% of U238

(a)

0.72, 99.28

(b)

99.28, 0.72

(c)

77.28, 72

(d)

72, 77.28

22. The specific characteristic of a common emitter amplifier is

(a)

High input resistance

(b)

Low power gain

(c)

Signal phase reversal

(d)

Low current gain

23. The combination of NAND gates here under are equivalent to:

(a)

OR gate and NOT gate

(b)

AND gate and OR gate

(c)

AND gate and NOT gate

(d)

OR gate and AND gate

24. The particle which gives mass to protons and neutrons are

(a)

Higgs particle

(b)

Einstein particle

(c)

Nanoparticle

(d)

Bulk particle

25. The internationally accepted frequency deviation for the purpose of FM broadcasts

(a)

75 kHz

(b)

68 kHz

(c)

80 kHz

(d)

70 kHz